In a silicon semiconductor integrated circuit (LSI), aluminum (Al) or Al alloy has been widely used as an electric conducting material. Along with development of finer patterning processing of the LSIs, copper (Cu) has come to be used as the electric conducting material, in order for achieving a reduction in the line resistance of the interconnections as well as a higher reliability thereof. Since Cu is likely to be diffused into a silicon oxide film, a conductive barrier metal film for preventing the diffusion of Cu has been used on the side surface and bottom surface of the Cu interconnections, whereas an insulating barrier film has been used on the top surface of the Cu interconnections.
Along with the recent development of the finer patterning in the LSIs, the dimension of the interconnections has been further reduced, thereby raising the problem of an increase in the inter-line capacitance. This led to development of introduction of a porous low-dielectric-constant film among the interlevel dielectric films. This is because the finer patterning as well as the lower dielectric constant of the interlevel dielectric film obtained by using a multilayer interconnection structure in the semiconductor device is effective to connection with a higher speed and a lower power consumption, and thus it is desired to achieve both the finer patterning and lower dielectric constant.
For achieving the lower dielectric constant for the interlayer dielectric film, a technique of raising the porosity of the film property by inserting and extracting porogen as well as introduction of hydrocarbon has been tried. Examples of the lower-dielectric-constant film include a hydrogen silsesquioxane film, a CDO (carbon-doped oxide) film, and an organic film. These films are formed using a spin-coating or chemical vapor deposition technique. Patent Publication JP-2004-289105A describes a technique of forming a porous insulation film by using a plasma-enhanced CVD technique. Republished Patent Publication JP-2002-526916A describes a method for forming a porous insulation film by using cyclic organic siloxane.
The present inventor considered the conventional techniques in the following way. If the technique described in JP-2004-289105A is used, since this uses a cut-and-coupling-type filming process wherein the monomer material is decomposed in plasma, the hydrocarbon component coupled to the monomer material is desorbed, thereby causing the problem that the relative permittivity is not lowered. In the technique described in Republished Patent Publication 2002-526916A and using cyclic siloxane monomer material, the cyclic structure of siloxane configures the skeletal frame thereof, which provides a relative permittivity of about 2.6. In addition, the siloxane including isopropyl group in a side chain causes a steric constraint, and if a vinyl group is included in a side chain thereof, it accelerates addition reaction of the monomer, to thereby provide a relative permittivity of about 2.5. However, there is a problem in the film strength thereof.
Further, along with the development of lower dielectric constant of the film, the porosity of the film increases, an thus results in a further reduction in the film strength. The reduction in the film strength accompanies reduction in the adhesive property between films to thereby degrade the device reliability.